Erlang has proven performance and reliability and now, the Elixir language and the Phoenix framework have made that platform viable for web application development. The "Programming Phoenix" book from the Pragmatic Programmers includes some performance benchmarks which show Phoenix compares favorably to frameworks & platforms that offer similar functionality.
I went to google to verify the benchmarks shown in the book and, though interesting, the bloggers' impressions of Elixir had as much to say about Elixir as the benchmarks so I am quoting them here:
"The default performance of Phoenix/Elixir is quite impressive, especially for such young projects. Given that Elixir is also one of the most conceptually enjoyable languages that I've personally coded with in years, I'm pretty bullish about their future." See Phoenix Showdown
"The ruby language and the Rails framework completely changed the way web applications were built; it started a religion of values that the community cared about" ... but now, "CRUD apps are a commodity these days. The fact that WebSockets, processes, and concurrency in Phoenix and Elixir are cheap, without sacrificing developer happiness is an absolute game-changer. I totally love Ruby on Rails. It completely changed the way that people thought about building web applications from 2005–2014.
I expect Elixir and Phoenix to have a similar impact from 2015–2025." See Why I'm Betting on Elixir
"Elixir provides the joy and productivity of Ruby with the concurrency and fault-tolerance of Erlang." See Elixir vs Ruby Showdown